pvl_calcPwat

Calculates precipitable water (cm) from ambient air temperature (C) and relatively humidity (%).

Contents

Syntax

Description

Calculates precipitable water (cm) from ambient air temperature (C) and relatively humidity (%) using an empirical model [1]. The model was developed by expanding Eq. 1 in [2]:

$$w = 0.1 H_v \rho_v$$

using Eq. 2 in [2]

$$\rho_v = 216.7 {\frac{RH}{T}} e_s$$

$H_v$ is the apparant water vapor scale height (km). The expression for $H_v$ is Eq. 4 in [2]:

$$H_v = 0.4976 + 1.5265{\frac{T}{273.15}} + \exp(13.6897 {\frac{T}{273.15}} - 14.9188{\frac{T}{273.15}}^3)$$

$\rho_v$ is the surface water vapor density (g/m^3). In the expression $\rho_v$, $e_s$ is the saturation water vapor pressure (millibar). The expression for $e_s$ is Eq. 1 in [3]

$$e_s = \exp(22.330 - 49.140{\frac{100}{T}} - 10.922{\frac{100}{T}}^2 - 0.39015{\frac{T}{100}}$$

Inputs

Output

Example

 [Pwat] = pvl_calcPwat(25,70) %Pressure at STC temperature and RH of 70%
Pwat =

    3.5090

Reference:

[1] W. M. Keogh and A. W. Blakers, Accurate Measurement, Using Natural Sunlight, of Silicon Solar Cells, Prog. in Photovoltaics: Res. and Appl. 2004, vol 12, pp. 1-19 (doi: 10.1002/pip.517).

% [2]   C. Gueymard, Analysis of Monthly Average Atmospheric Precipitable
%           Water and Turbidity in Canada and Northern United States,
%           Solar Energy vol 53(1), pp. 57-71, 1994.
%           (doi:10.1016/S0038-092X(94)90606-8).

% [3]   C. Gueymard, Assessment of the Accuracy and Computing Speed of
%           simplified saturation vapor equations using a new reference
%           dataset, J. of Applied Meteorology 1993, vol. 32(7), pp.
%           1294-1300 (doi:
%           10.1175/1520-0450(1993)032<1294:AOTAAC>2.0.CO;2).

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